The present invention relates to a barrier stack used in, for example, integrated circuits (ICs) which reduces diffusion of atoms or molecules, such as oxygen. More particularly, the barrier stack reduces oxidation of the plug in capacitor over plug structures.
Memory ICs comprise a plurality of memory cells interconnected by bitlines and wordlines. A memory cell includes a transistor coupled to a capacitor for storage of a bit of information. To realize high density memory ICs, the memory cells employ a capacitor-over-plug (COP) structure, as shown in FIG. 1. The structure includes a capacitor 140 having a dielectric layer 146 located between first and second electrodes 141 and 142. The capacitor is coupled to a conductive plug 170.
Typically, a high temperature anneal in an oxygen (O2) ambient is required to improve the properties of the dielectric layer, particularly for high k dielectric and ferroelectric materials. Additionally, another anneal in O2 is required to repair the damage caused by etching of the contact hole 165. Typically, the anneals are performed at 700xc2x0 C. for 1 hour. During the anneals, O2 diffuses through the capacitor and oxidizes the plug. This can lead to performance degradation and, in some cases, failures as a result of increased plug resistivity or electrical open connections.
To prevent diffusion of oxygen through the capacitor, a barrier layer 187 formed from iridium is provided between the lower electrode and the plug. Iridium (Ir) is used due to its good barrier properties against O2. Since Ir has a tendency to delaminate from the ILD layer (e.g., silicon dioxide or silicon nitride), a titanium nitride layer 182 is provided between the layers to promote adhesion. However, as shown, sidewalls of the barrier and adhesion layers are exposed. Oxygen can diffuse through the exposed sidewalls and horizontally along the interfaces between the adhesion, barrier, and ILD, oxidizing the adhesion layer, in some cases, the plug.
From the foregoing discussion, it is desirable to provide an improved barrier layer for reducing oxidation of the plug in a capacitor over plug structure.
The invention relates generally to the formation of capacitors over plug structures. In one embodiment, an improved barrier stack which reduces oxidation of the plug is described. The barrier stack is located between an adhesion layer and a capacitor to reduce oxidation of the plug.
In one embodiment, a non-conductive adhesion layer is provided on an interlevel dielectric layer except where the plug is located. The adhesion layer, in one embodiment, comprises titanium oxide. First and second conductive barrier layers are provided between the adhesion layer and the capacitor. The first barrier layer is disposed between the second barrier layer and adhesion layer. The second barrier layer covers the top surface and sidewalls of the first barrier layer. In one embodiment, the first barrier layer comprises Ir and the second barrier layer comprises IrOx. The second barrier layer inhibits the diffusion of, for example, O2 through the sidewalls of the first barrier layer and interface of the adhesion and first barrier layer, thereby reducing or avoiding plug oxidation.